Doctor of Philosophy (PhD)
Physics and Astronomy
Knowledge of stellar nuclear reaction rates is critical to understanding the cosmic origins of the abundances of elements. In order to determine these reaction rates, accurate measurements of nuclear cross sections are needed. This thesis presents the results of an experiment to directly measure the neutron capture cross sections of 70-Ge, 72-Ge, 74-Ge, and 76-Ge. These measurements were performed at the Los Alamos Neutron Science CEnter (LANSCE) using the Detector for Advanced Neutron Capture Experiments (DANCE). This is the first direct measurement for many of these isotopes across the neutron energy spectrum of 10 eV to 1 MeV using the neutron time-of-flight method. Maxwellian-Averaged Cross Sections (MACS) were calculated from these measurements at the astrophysically relevant temperatures in order to determine the stellar nuclear reaction rates. The results of this experiment are neutron capture cross sections and MACS for 70-, 72-, 74-, 76-Ge with uncertainties on the order of 5%. A comparison of these values to the current evaluated cross sections in two databases is also presented.
In addition to the experimental component of my thesis, a series of simulations were performed in the pursuit of designing a next-generation ion trap named the BEtA-Recoil trap (BEARtrap). BEARtrap was designed for beta-delayed neutron emission studies. It is a linear Paul trap surrounded by an array of MCP detectors and plastic scintillator detectors. beta-delayed neutron emission affects the abundance curves for heavy elements created in the r-process, comprises a major component of nuclear reactor neutron fluxes, and has national security applications. BEARtrap allows for a novel technique to simultaneously measure the beta-delayed neutron emission branching ratios and emitted neutron energy spectra by means of beta-recoil ion coincident detection.
Laminack, Alexander, "Stellar Nucleosynthesis: Direct Measurement of the Neutron-Capture Cross Sections of Stable Germanium Isotopes and Design of a Next Generation Ion Trap for the Study of Beta-Delayed Neutron Emission" (2020). LSU Doctoral Dissertations. 5131.